1. Field of the Invention
The present invention generally relates to a backlight module, and more particularly, to a light guide plate (LGP) applied to a backlight module.
2. Description of Related Art
FIG. 1 is a cross-sectional diagram of a conventional backlight module, FIG. 2 is a locally-enlarged cross-sectional diagram of the prism pattern in FIG. 1 and FIG. 3 is a curve chart showing the relationship between the luminance and the light emitting angle of the light emitting surface of the LGP in FIG. 1. Referring to FIG. 1, a backlight module 100 includes a light source 110, a reflective sheet 120 and an LGP 200. The light source 110 is disposed adjacent to a light incident surface 210 of the LGP 200 and the reflective sheet 120 is adjacent to a bottom surface 220 of the LGP 200. The light provided by the light source 110 travels into the LGP 200 through the light incident surface 210 and then travels out through a light emitting surface 230 of the LGP 200, so as to form a planar light source, and then travels to a liquid crystal display panel (LCD panel, not shown herein) on the light emitting surface 230. The reflective sheet 120 may reflect the light to the light emitting surface 230.
Referring to FIGS. 1 and 2, the bottom surface 220 of the LGP 200 has a plurality of flat surfaces 240 and a plurality of prism patterns 250 disposed alternately with the flat surfaces 240, and each prism pattern 250 is composed of a first slanted surface 252, a second slanted surface 254 and a third slanted surface 256. When the light traveling into the LGP 200 through the light incident surface 210 is transmitted to the first slanted surface 252, a part of the light is totally reflected and then travels to the LCD panel through the light emitting surface 230. Referring to FIG. 3, as the light travels out through the light emitting surface 230 (FIG. 1), the luminance of the light between the light emitting angle of −30° and the light emitting angle of 30° is relatively great, so that each distribution curve on the curve chart of luminance vs. light emitting angle has a peak between the light emitting angle of −30° and the light emitting angle of 30°.
Referring to FIGS. 2 and 3 again, each distribution curve in FIG. 3 represents a ratio of a base length c to a base length b. The distribution curves G1-G4 in FIG. 3 respectively represent c:b=1:1, c:b=4:3, c:b=2:1 and c:b=4:1. However, in the conventional LGP 200, each distribution curve has another peak between the light emitting angle of 30° and the light emitting angle of 90°. Therefore, when the conventional LGP 200 is used to provide a planar light source, the light travelling from the light emitting surface 230 is less concentrated and the luminance efficiency thereof is lower.